Growth factors play an important role in supraspinatus tendon-to-bone healing. The objective of this study was to evaluate the temporal expression of 8 different growth factors in tendon-to-bone healing in an animal model. We hypothesize that growth factors exhibit unique temporal profiles that correlate to specific stages in the acute process of the supraspinatus tendon. To test this hypothesis, rats underwent bilateral supraspinatus tendon detachment and repair. Animals were euthanized at 1, 2, 4, 8, and 16 weeks. Immunohistochemical staining was done using antibodies for basic fibroblast growth factor (bFGF), bone morphogenetic protein 12 (BMP-12), BMP-13, BMP-14, cartilage oligomeric matrix protein (COMP), connective tissue growth factor (CTGF), platelet-derived growth factor-B (PDGF-B), and transforming growth factor-beta1 (TGF-beta1). Immunoassays showed an increase in the expression of all growth factors at 1 week, followed by a return to control or undetectable levels by 16 weeks in both the insertion and midsubstance. Future studies will investigate the different impacts of growth factor expression in tendon to bone healing.

The reported biomechanical principles of Dynesys do not reflect advantages in outcome compared with none or others stabilization systems after microsurgical radicular decompression reported in the literature.

Study Design Controlled Laboratory Study Objectives To measure the architectural properties of rat supraspinatus muscle after a complete detachment of its distal tendon. Methods Supraspinatus muscles were released from the left humerus of 29 rats (Sprague-Dawley, mass 400 - 450 g) and animals were returned to cage activity for 2 weeks (n = 12), 4 weeks (n = 9), or 9 weeks (n=8) before euthanasia. Measurements of muscle mass, pennation angle, fiber bundle length (sarcomere number), and sarcomere length permitted calculation of normalized fiber length, serial sarcomere number, and physiological cross-sectional area (PCSA). Results Coronal oblique sections of the supraspinatus confirmed surgical transection of the supraspinatus muscle at 2 weeks, with reattachment by 4 weeks. Muscle mass and length were significantly lower in released muscles at 2 weeks, 4 weeks, and 9 weeks. Sarcomere lengths in released muscles were significantly shorter at 2 weeks but not different by 4 weeks. Sarcomere number was significantly reduced at 2 and 4 weeks, but returned to control values by 9 weeks. The opposing effects of smaller mass and shorter fibers produced significantly smaller PCSA at 2 weeks, but PCSA returned to control levels by 4 weeks. Conclusions Release of the supraspinatus muscle produced early radial and longitudinal atrophy of the muscle. The functional implications of these adaptations would be most profound at early time points (particularly relevant for rehabilitation), when the muscle remains smaller in cross-sectional area and, due to reduced sarcomere number, would be forced to operate over a wider range of the length-tension curve and at higher velocities, all adaptations resulting in compromised force generating capacity. These data are relevant to physical therapy because they provide tissue-level insights into impaired muscle and shoulder function following rotator cuff injury.

Rotator cuff tears are a common clinical problem that can result in pain and disability. Previous studies in a rat model showed enhanced tendon to bone healing with postoperative immobilization. The objective of this study was to determine the effect of postimmobilization activity level on insertion site properties and joint mechanics in a rat model. Our hypothesis was that exercise following a short period of immobilization will cause detrimental changes in insertion site properties compared to cage activity following the same period of immobilization, but that passive shoulder mechanics will not be affected. We detached and repaired the supraspinatus tendon of 22 Sprague-Dawley rats, and the injured shoulder was immobilized postoperatively for 2 weeks. Following immobilization, rats were prescribed cage activity or exercise for 12 weeks. Passive shoulder mechanics were determined, and following euthansia, tendon cross-sectional area and mechanical properties were measured. Exercise following immobilization resulted in significant decreases compared to cage activity in range of motion, tendon stiffness, modulus, percent relaxation, and several parameters from both a structurally based elastic model and a quasilinear viscoelastic model. Therefore, we conclude that after a short period of immobilization, increased activity is detrimental to both tendon mechanical properties and shoulder joint mechanics, presumably due to increased scar production. ß